The UK High Court has issued a ruling that a tweet posted by Sally Bercow about retired politician Lord McAlpine was libellous; the latest in a string of social media lawsuits.

The BBC caused controversy when its Newsnight programme made allegations against a “leading Conservative politician,” suggesting he was involved in a child sex abuse scandal. McAlpine was not named in the show, but speculation was rampant on social media and he ended up being one of those wrongly accused.

Many people tweeted their suspicions of who the top Tory politician could be, with McAlpine's name featuring among numerous tweets. Bercow, the wife of the Commons Speakers John Bercow, tweeted two days after the show: “Why is Lord McAlpine trending? *innocent face*.”

While not an outright allegation of improper behaviour, the High Court ruled that this tweet wrongly implied that McAlpine was a paedophile. Justice Tugendhat said the comment featured an innuendo that carried the “same effect” as the natural meaning of the words.

Bercow denied her tweet was defamatory, but acknowledged deep regret about posting it. She reiterated her apologies to McAlpine and his family. She will be required to make a formal apology in court and an undisclosed payment to a charity of McAlpine's choice.

The man who accused McAlpine of sexual abuse later admitted that it was a case of mistaken identity, but the public commentary on the issue had already caused undue damage to McAlpine's reputation.

The case highlights the ignorance of many using social media about the potential legal consequences of making insinuations or allegations about politicians, celebrities, or members of the general public.